1. Field of the Invention
The present invention relates to a low dielectric composition, an insulating material, a sealing material, and a circuit board. More particularly, the present invention relates to a low dielectric composition exhibiting superior insulation properties and capable of producing an insulating material and sealing material with a low dielectric constant and low dielectric loss tangent (tan .delta.), to an insulating material and a sealing material comprising the low dielectric composition, and to a circuit board provided with the insulating material or sealing material, in particular a circuit board exhibiting high reliability in the high frequency region.
2. Description of the Background Art
Laminated boards prepared from several sheets of prepregs by pressure-molding with heating is used as a substrate for electronic circuit boards. Such a prepreg is prepared by impregnating a glass fiber fabric substrate with a thermosetting resin such as epoxy resin or polyimide and drying the composite. Because such a laminated board has a high dielectric constant from 4.9 to 5.1, the resulting circuit board has a large electrostatic capacity, which causes generation of crosstalks among the circuits formed on the substrate. Such a laminated board is thus not necessarily satisfactory as a high frequency circuit board.
A method of filling a thermosetting resin with hollow glass particles has been proposed as a method for preparing laminated sheets for the circuit board with a low dielectric constant (Japanese Patent Applications Laid-open No. 49256/1981, No. 49257/1981, No. 138794/1993, and No. 46309/1996). According to this method, the dielectric constant of the laminated board is decreased due to the low dielectric constant of the gases such as air and nitrogen which are contained in the hollow glass particles.
In the preparation of the laminated board using this method, it is difficult to cause the hollow glass particles to homogeneously disperse in thermosetting resin due to inferior affinity of the hollow glass particles with the resin, resulting in laminated boards which contain voids. The use of laminated boards with voids contained therein is unsuitable for use as a material for circuit boards, since the mechanical strength of the substrates is remarkably impaired by such voids.
Due to the recent tendency of increased integration of circuit boards, a multi-layered circuit board prepared by laminating several substrates, each having circuits formed on the surface, has been developed. The substrates composing such a multi-layered circuit board should have more excellent insulation properties and a lower dielectric constant than the substrate for producing the above-mentioned monolayered circuit board.
The multi-layered circuit boards are provided with an insulating layer between the substrates to insulate the circuits so as to avoid contact of a circuit formed on the surface of one substrate with another circuit on another substrate. In addition, a sealing material layer is provided in the space between the circuit board and the semiconductor device which is produced when the semiconductor device is mounted on a mono-layer or multi-layer circuit board. Such a sealing material layer should have the same superior insulation properties and low dielectric constant as required for the substrates.
In recent years, a resin-sealed type using an epoxy resin composition has become the mainstream of semiconductor devices using semiconductor elements such as transistors, integrated circuits, and LSIs from the viewpoint of cost and mass production. Due to the high integration requirement brought about by the technological reform in the semi-conductor field which accelerated the requirement for a large element with minute wiring patterns, the tendency toward miniaturization and using thinner parts is also required for such a resin-sealed type of semi-conductor equipment. Greater reliability (such as decreased crosstalk and reduced heat generation) is required for the sealing material.
The present invention has been achieved in view of this situation and has an object of providing a low dielectric composition exhibiting superior insulation properties and capable of producing an insulating material and sealing material with a low dielectric constant and low dielectric loss tangent (tan .delta.), an insulating material and a sealing material comprising the low dielectric composition, and a circuit board provided with the insulating material or sealing material, particularly a circuit board exhibiting high reliability in the high frequency region.